The objective of this work is to define the specific type of damage to DNA caused by antitumor drugs and to elucidate the mechanisms by which such lesions are enzymatically repaired in mammalian cells. Specific aims include: to determine the nucleotides or sequences altered by chemotherapeutic agents such as the alkylating and antibiotic agents and hydrazine derivatives; to characterize the structure of the damaged DNA; to utilize activating enzymes to extent the range of the studies; to study the distribution of specific activating activities in normal and in tumor tissues; to characterize the action of purified repair enzymes on DNA damaged by chemotherapeutic agents; to delineate repair pathways for DNA modified by chemotherapeutic agents in extracts of mammalian cells; to develop assays for new mammalian repair activities. These studies will exploit DNA sequencing techniques and the use of DNA fragments of defined sequence to precisely define the process of damage and repair of DNA.